Engine boost may be controlled by adjusting an amount of gas flowing through a turbine of a turbocharger, for example via a waste gate. In one example, a waste gate may include a waste gate valve and a valve seat. The waste gate valve may be actuated by an associated electric actuator. The electric actuator may be controlled to adjust a waste gate valve position, thereby controlling the amount of gas flowing through the turbine and achieving the desired boost. Electric waste gate actuation may provide a faster response and more precise position control relative to a pneumatically-actuated waste gate. The faster response and more precise control may increase engine efficiency, fuel efficiency and emissions control.
In one example, an electric actuator that is used to control the position of a waste gate valve includes an electric motor which transmits a force to a plurality of linkages that are coupled to the waste gate valve. The plurality of linkages directly actuates the waste gate valve to adjust the waste gate valve position. The plurality of linkages allows the electric motor to be positioned remotely from an exhaust passage where the waste gate is located so as to reduce the likelihood of degradation of the electric motor due to heat exposure. The electric motor is controlled based on feedback from a position sensor that is coupled to a gear box output shaft and provides an indication of a waste gate valve position.
However, the inventors herein have identified some potential issues with such an approach. For example, although the gear box output shaft sensor provides gear box output shaft position detection, and the waste gate valve is adjusted based on information of the gear box output shaft position, the sensor provides no indication of an end-stop of the waste gate. In particular, an end-stop of the waste gate may include a position where the waste gate valve suitably aligns with the valve seat to substantially prevent gas from flowing through the waste gate. On the other hand, the end-stop may include a position where the waste gate valve is fully open.
In the above described approach, the gear box output shaft sensor does not provide an indication of the waste gate valve position relative to a valve seat position. Without knowing the end-stop of the waste gate valve, when the waste gate valve is commanded to a closed position the waste gate valve position may be adjusted too much causing the waste gate valve to impact the valve seat at a high velocity. By adjusting the waste gate valve too much, noise, vibration, harshness (NVH) conditions and wear on the valve seat may be increased. In addition, the closed-loop control system may apply too much current to the waste gate trying to move the waste gate valve to a desired stop position that is physically impossible to reach, leading to high stress in the whole system. On the other hand, the waste gate valve position may be adjusted too little causing the waste gate valve to not properly seal with the valve seat resulting in undesired flow of gas through the waste gate that reduces boost pressure.
Furthermore, the waste gate valve and the plurality of linkages may be exposed to high temperatures within the turbine that can affect accuracy of the position sensor output. For example, the plurality of linkages changes length as temperature changes. Under some conditions, such changes in length may cause the end-stop position of the waste gate valve to be reached before that position is indicated by the gear box output shaft sensor.
Thus in one example, some of the above issues may be at least partly addressed by a method, comprising: during calibration of a waste gate position sensor: adjusting a waste gate valve to a first end-stop position, associating a first feedback position with the first end-stop position, adjusting the waste gate valve to a second end-stop position, associating a second feedback position with the second end-stop position, and adjusting a position sensor gain based on the first feedback position and the second feedback position.
By detecting an end-stop (valve seat) position of the waste gate valve and providing feedback control of the waste gate valve relative to the end-stop position, control accuracy with respect to aligning the waste gate valve with a valve seat to close the waste gate may be increased. In this way, high impact between the waste gate valve and the valve seat will be reduced and NVH conditions may be reduced. Moreover, the end stop detection and corresponding position sensor calibration may increase waste gate lift control accuracy, which in turn may increase boost control accuracy.
It will be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description, which follows. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined by the claims that follow the detailed description. Further, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.